Open Track is an application that allows the use of the Oculus Rift tracker to simulate other tracking methods.
Use With GamesEdit
For the most part most games you'll have to use mouse emulation. It's not the best, but most games don't support anything else.
Luckily, ArmA 3 supports freetrack! So if we want to use this with the Oculus Rift, on the OpenTrack window select the "Protocol" dropdown, then select "freetrack 2.0 enchanced". Start it up, load up ArmA 3, then get into a game and you should be able to look around with the Rift.
For most everything else, set the protocol to mouse emulation.